One method to operate an internal combustion engine during the regeneration of a NOx, trap is presented in Patent Application No. 2005/0022503 A1. In particular, this method presents a way to control the engine when the exhaust gas air-fuel mixture is enriched to promote NOx trap regeneration. In one example, the method adjusts an excess air ratio λ and fuel injection timing during NOx, trap regeneration by controlling fuel injection timing, intake air throttle opening amount, and an opening amount of an exhaust gas recirculation (EGR) valve. In particular, the opening amounts of the intake throttle and the EGR valve are adjusted to enrich the engine air-fuel mixture during the regeneration of the NOx trap. Further, the method adjusts injection timing based on engine speed and boost pressure (i.e., the difference between atmospheric pressure and the pressure in the intake manifold). However, the method does not measure boost pressure directly because there can be a delay between throttle movement and an actual change in the boost pressure. Rather, the method infers boost pressure from measured throttle opening amount and measured EGR valve opening amount so as to reduce the before-mentioned delay. In addition, the method adjusts injection timing in an attempt to control engine torque fluctuations that can accompany adjusting the cylinder air-fuel mixture as described by the method. Furthermore, the base fuel amount can be adjusted based on λ, EGR, and engine coolant temperature and can be further adjusted in response to the boost pressure and engine speed.
The above-mentioned method can also have several disadvantages. For example, the throttle and EGR valve positions are used to predict boost pressure, but the valve positions may not be indicative of the actual boost pressure because of manufacturing tolerances and/or component degradation. This can increase air-fuel mixture error and may reduce the effectiveness of the after treatment regeneration process. Further, the engine torque control may degrade since engine torque can be related to fuel injection timing and since the method determines injection timing from an inferred boost pressure.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method to control an engine during the regeneration of an exhaust gas after treatment device that offers substantial improvements.